DE3328342A1 - Method of soldering chip components onto printed circuit boards - Google Patents

Abstract

To solder chip components onto printed circuit boards, an electrodeposited solder layer which is approximately 10-100 mu m thick and also serves as a mask while the conductor track pattern is being etched out and as a source of solder is first deposited on the printed circuit board coated with the conductor track metallization. After coating the printed circuit boards, in particular the contact pads of the conductor tracks for the chip components, with a highly viscous colophonium solution, the chip components are placed on the contact pads and connected by reflow soldering. With this method it is also possible to use chip components and lead components simultaneously, plated-through holes being provided for the lead components. It is also possible to carry out double-sided chip mounting on the printed circuit boards by first mounting chip components on one side and then on the other side, the colophonium film acting as an adhesive prior to reflow soldering and as a flux during reflow soldering.

Description

Method for soldering chip components on conductor

prior art panels The invention is based on a method according to the genre of the main claim. It is known the necessary for a circuit First glue chip components to the solder side of the circuit board, the glue then to cure and then the chip components by surge, drag or contact immersion soldering.

However, this method has the disadvantage that only one one-sided assembly two process steps, namely gluing with curing as well the soldering, are necessary and that with the three mentioned soldering processes with accordingly equipped solder baths or

Soldering systems Gaps between the conductor track end areas of only 0.3 ... 0.4 mm, which limits the packing density of the circuit. - It is also known on the contact surfaces of the conductor tracks for the chip components Apply solder paste by screen printing, which is preferably done using thick-film technology is used to build hybrid circuits. The chip components are printed onto the pasty solder pad, which is a pulpy mixture of solder metal powder, solution and represents flux, put on, fixed by the pulpy state and soldered in by subsequent reflow soldering.

This method has the disadvantage that an additional screen printing process with the solder paste is required. If the panels are fitted on both sides, this way very complicated. Furthermore, the solder pads must not be too thin and therefore require the avoidance of close-meshed screens when printing, which makes the realization fine contact surface structures becomes difficult. After all, it comes with melting the solder pad easy to splatter, with stray solder balls on the circuit arise that lead to the formation of electrical shunts or short circuits can. - Finally, it is known, the contact surfaces of the conductor tracks for the Chip components on the circuit boards (such as conventional circuit boards, thick-film or thin-film circuits) initially in a first stage by surge, drag or dip soldering to cover with solder pads, then the chip components with their Put contact surfaces on the conductor track end areas and use viscous To fix the rosin solution and then with a subsequent second heat treatment, z. B. in a continuous furnace, as the second stage, the chip components in the circuits to solder. The disadvantage of this process is that two heating processes are required are that the applied solder pads have curved and spherical surfaces, whereby the chip components tend to slide sideways when placed, and that the thickness of the solder pads and thus the amount of that present during reflow soldering Lot is subject to a certain spread, which is difficult to get under control is.

Advantages of the invention The method according to the invention with the characterizing Features of the main claim has the advantage over this that it the production of printed circuits in chip design is significantly simplified and that it makes a greater miniaturization possible, because with this process distances the contact areas of the conductor tracks for the chip components and the conductor tracks even down to 0.1 ... 0.2 mm can be implemented without difficulty, without soldering difficulties occurring.

This naturally leads to a high packing density of the components. Wide and narrow as well as high and low components can be closely spaced with only narrow spaces are placed, because the required solder as galvanic Layer on the contact surfaces of the conductor tracks for the chip components on the The circuit board is already there and not as with conventional soldering processes must be supplied via the free spaces as a liquid melt, which at very narrow spaces due to the solder-repellent effect due to non-wetting the insulating component surfaces no longer succeed or if the distance is slightly wider easily leads to bridging. When using open components such as B.

Potentiometers or trimming capacitors, the method is just as advantageous, because with the conventional soldering process without special protective measures, the There is a risk that these parts will be damaged or electrically short-circuited and thus become unusable.

The measures listed in the subclaims are advantageous Further training and improvements to the method specified in the main claim are possible. It is particularly advantageous that the method can also be used for combined equipping Use of Xe 'ers'atten with ohio components and wire components neon each other can be made by making plated through holes for the wire components intended and after the galvanic solder layer has been applied and the PCB contacted both types of components at the same time by reflow soldering can be. This is particularly advantageous as long as certain types of components are not yet offered in chip form. It is also advantageous that the method in a simple way also for the double-sided assembly of printed circuit boards with chip and wire components can be used.

The deposition of a galvanic solder layer is part of the usual manufacturing process of circuit boards coated on both sides with plated-through holes according to the semi-additive or additive processes are known per se.

It serves as a mask when etching out the conductor track image (structure etching the circuit board) and is about 7-15 / µm thick. Will this galvanic solder layer according to the method according to the invention also as a solder source Used for reflow soldering when soldering in the components, their thickness must be approx. 10 ...

100 µm to be reinforced to provide both functions - anti-etch protection and solder source - to be able to fulfill at the same time.

3 DESCRIPTION OF THE EXEMPLARY EMBODIMENTS For the production of a with components In chip form assembled circuit board is first the circuit after the semi-additive or additive processes.

The printed circuit board circuit prepared in this way is then known per se Way provided in an electroplating bath with a lead-tin layer that has a thickness of about 10 ... 100 µm and at the same time as a mask when etching out the conductor track image and serves as a solder source.

After etching out the track pattern, the circuit boards, preferably but the contact areas of the conductor tracks for the chip components with the whole area Coated with a viscous rosin solution that doubles as an adhesive to hold the components in place after they have been put on and later when soldering in as a flux serves. Then the chip components are placed on the intended contact surfaces of the conductor tracks placed for the chip components, possibly dried briefly in air at approx. 100 OC and then by reflow soldering, e.g. B.

by placing in a continuous furnace at a temperature above the melting point of the PbSn alloy mechanically and electrically contacted. - The galvanic solder layer results on the contact surfaces of the conductor tracks for the chip components the solder pads required for soldering the components. Through the galvanic Deposition, the evenness is largely retained. The solder pads are on hers Upper side also smooth and flat, which means that the planar chip components can be placed on top with their flat contact surfaces is facilitated. - To achieve a special good soldering quality, it is advantageous to reflow soldering in an oxygen-free Carry out atmosphere from an inert or activated protective gas.

The method just described can be used on a printed circuit board also use chip and wire components side by side. This can be B. necessary because certain types of components are not yet available in chip form. The circuit boards are then with flat contact surfaces of the conductor tracks for the Chip components and plated through holes provided in the required number. In the subsequent galvanic solder application, which takes place as described above, the plated-through holes remain open. Then the circuit boards, preferably the contact surfaces of the Conductor tracks for the chip components and the plated-through holes are coated over the whole area with rosin solution, the chip components on the flat contact surfaces of the conductor tracks for the chip components put on and the wire components inserted into the plated-through holes. Then the reflow soldering takes place, e.g. B.

again in a conveyor oven as described above. To at this A variant to achieve a good solder filling in the holes, the geometries be coordinated with each other: hole diameter, wire diameter, plate thickness, The thickness of the galvanic solder layer and the size of the soldering eye must be selected so that that during reflow soldering the hole is filled as completely as possible with the amount of solder present will. If that does not work, for example because of the difference between the hole diameter and wire diameter is too large, can be done by a selective solder reinforcement, z. B. with solder paste in screen printing, with suitable solder preforms or with an additional one galvanic deposition at the corresponding holes and / or wire connections so much solder is provided that a complete filling during reflow soldering is made possible. However, since this requires additional effort, it is on In any case cheaper, special care is taken in the mutual coordination of the geometries to use. This also applies analogously to the geometric adaptation of the contact surfaces of the conductor tracks for the chip components (landing areas) to the size of the contact areas of the chip components used. But here too, if necessary, a selective Solder reinforcement as described above, a better solder filling can be achieved.

With the double-sided chip assembly of the circuit boards with subsequent Reflow soldering what after this procedure also without the use Additional solder is possible, care must be taken that the chip components the underside does not fall off again during the assembly of the upper side. For this The thick liquid described above, used as an adhesive and flux at the same time, is sufficient Kolophoniumfik, since the usual chip components are relatively small and very light and after the rosin has dried at approx. 100 OC they adhere so firmly that the printed circuit board, which was initially populated on one side, was easily turned over and then opened the still empty back can be filled in the same way. After that, will again briefly dried at approx. 100 ° C. and the rosin thickened and hardened. In this state the assembled circuit board is so stable that it can be reflow soldered can also be stored for some time. The chip components are then used during reflow soldering soldered on the top and bottom at the same time.

If relatively large and heavy components are used in special cases, in which the adhesion with the rosin is not sufficient, this can be done in a well-known When assembling, first apply a suitable adhesive to the dry and clean PCB can be glued on (the same technique as mentioned at the beginning Wave soldering of chip components). After the adhesive has solidified (hardened) Then comes the application of the viscous rosin film (also over the previously glued Components away, it is needed there as a flux) and the assembly oit the usual lightweight chip components in the manner described above.

The term printed circuit board used here is in the broadest sense for to understand all substrates that have a layer structure and a structure in enable the manner described and as circuit boards for electronic circuits come into question. This not only includes the conventional copper-coated plates made of phenolic and epoxy hard paper as well as epoxy glass hard fabric (e.g. 3.FR2-, FR3 and FR \ 4 materials), but also, for example, multilayer, flexible circuits, Panels made of ceramic or glass as well as insulated metal core panels that only cover the entire surface with a suitable adhesive and conductive layer, then with a structure mask and then successively coated with copper and solder and then structure-etched. Instead of Another suitable conductor metal, such as e.g. B.

Nickel, can be used. - Since the substrates sector is currently in motion is, there are some application-technical innovations here in the next few years expect.

The galvanic solder layer described here preferably exists made of lead and tin, according to the current electroplating standard. the Solder layer kri as an alloy, but also as a combination of an alloy and a tin and / or lead layer are deposited. Also pure tin or Lead layers alone are possible. In all cases this results in solder layers, which are to be used in the sense of the described registration.

With the advancement of electroplating technology it is to be expected that too other metals such as B. indium, silver, cadmium, anion and the like in different Quantity can be built into the solder layer and thus solder layers arise, which are even better suited for reflow soldering electronic circuits and can be used more advantageously than the PbSn solder that is now available. These too Solder layers to be expected later are to be used in the sense of the application and should be included in this.

Claims (6)

Claims 1. A method for soldering chip components on circuit boards, in which first a layer of solder on the with a conductor track metallization, such as Copper, occupied circuit board is applied and the chip components by reflow soldering are contacted, characterized in that the solder layer is applied galvanically is that then the circuit boards, in particular the contact surfaces of the conductor tracks for the chip components coated with a rosin solution, the chip components placed on these contact surfaces and finally contacted by reflow soldering will. 2. The method according to claim 1, characterized in that the reflow soldering is carried out in an oxygen-free atmosphere. 3. The method according to claim 1, characterized in that at the same time Use of chip components and wire components for the chip components level Contact surfaces, for the wire components, on the other hand, through-plated holes are provided that a layer of solder is electrodeposited on the conductor track metallization becomes that after coating contact surfaces and holes with rosin solution the chip components on the contact surfaces put on and the wire components inserted into the holes and finally contacted the components by reflow soldering will. 4. The method according to claim 3, characterized in that to the complete Closing the holes in the wire components or filling the solder joints more fully In addition, a selective solder reinforcement on special chip components during reflow soldering with the solder paste, with solder preforms or by galvanic deposition at the holes and / or the flat contact surfaces and / or the component connections will. 5. The method according to claim 1, characterized in that with double-sided Chip assembly of the circuit boards, the galvanic solder layer is applied on both sides is that then first on the underside of the circuit boards, in particular the contact surfaces the conductor tracks for the chip components are coated with rosin solution and then the chip components on the contact surfaces of the conductor tracks for the chip components put on and dried at about 100 0C and that after drying of the Rosin film the tops of the circuit boards by coating them with rosin solution and placing the chip components and drying them at approx. 100 ° C placing them in the same place Way and finally the chip components of both sides in one Reflow soldering process are contacted. 6. The method according to any one of claims 1 to 5, characterized in that that the galvanic solder layer is applied in a thickness of approx. 10 ... 100 μm will.